Copolymers of unsaturated fatty esters, their use as viscosity improver and lubricating oil containing said copolymers

ABSTRACT

Copolymers of unsaturated fatty esters capable of being obtained by copolymerization in a mineral oil of a percentage a) of an ester of a carboxylic acid A 1 , of a percentage b) of an ester of a carboxylic acid A 2  and a percentage c) of an ester of a carboxylic acid A 3 , wherein a), is between 12 and 20%, c) is between 14 and 30% and b), which is preferably 72 and 45%, is such that a)+b)+c)=100%. The copolymers in accordance with the invention are reemployed as viscosity improver in lubricating oils.

FIELD OF THE INVENTION

The invention relates to copolymers of unsaturated fatty esters.

It also relates to the use of these copolymers as viscosity improversfor lubricating oils at high temperatures without adversely affectingviscosity at low temperatures.

Finally, it relates to a composition which is based on theabove-mentioned copolymers and which is intended to be incorporated intolubricating oils, as well as to the lubricating oils comprising saidcopolymers or said composition.

BACKGROUND OF THE INVENTION

The lubricating oils in question within the scope of the presentinvention consist essentially of naphthenic hydrocarbons and paraffinichydrocarbons and their mixtures, the kinematic viscosity of these oilsat 100° C. being between about 1 and about 20 and, preferably betweenabout 2 and about 10 mm² /s.

There are already known copolymers of the kind in question which can beemployed as multipurpose agents and especially as viscosity improvers inlubricating oils.

It is found, however, that, as oil manufacturers' requirements becomeincreasingly constraining, copolymers which are already known no longermeet the requirements of practice, especially in their applications inso-called top-grade oils or in the case of highly specialized uses.

In addition, the multitude of factors that affect the properties of theabove-mentioned copolymers and the large number of possible combinationsof these factors mean that the search for copolymers capable ofimparting ever better properties to lubricating oils, especially inrespect of their viscosity, becomes increasingly difficult.

DETAILED DESCRIPTION OF THE INVENTION

It is therefore surprising to successfully prepare copolymers capable ofimparting to formulations based on lubricating oils a kinematicviscosity which is satisfactory not only at high temperature,particularly at 100° C., but also at low, or even very low temperature,40° C. and at temperatures reaching and even going beyond -30° C., thisviscosity satisfying conditions are at least equal to those of the ISOClassifications VG 32 which defines an industrial fluid lubricant havinga midpoint viscosity 32 centistokes (mm² /s) at 40° C. and kinematicviscosity between 28.8 and 35.2 centistokes at 40° C., described in thestandards ISO 34-48 or NF T60-141, and in ASTM Standard D-2422, themeasurements being carried out according to ASTM Procedure D 445,Standard Test Method for Kinematic Viscosity of Transparent and OpaqueLiquids. ASTM D-445 covers the determination of the kinematic viscosityof liquid petroleum products by measuring the time for a volume ofliquid to flow under gravity through a calibrated glass capillaryviscometer.

This procedure is given in the Annual Book of ASTM Standards which ispublished annually by ASTM, Philadelphia, Pa. 19103 USA.

SUMMARY OF THE INVENTION

The copolymers in accordance with the invention, which are copolymers ofunsaturated fatty esters capable of being obtained by copolymerization,conveniently in an organic diluent, preferably in a mineral oil

of a percentage a (expressed on mass basis) of an ester of a carboxylicacid A₁ containing from 3 to 5 carbon atoms and exhibits an ethylenicunsaturation alpha to the carboxylic functional group, with an alcohol,preferably a saturated alcohol, of formula R₁ OH containing from 1 to 3carbon atoms, preferably 1 or 2 carbon atoms, said alcohol beingadvantageously methyl alcohol,

of a percentage b (expressed on mass basis) of an ester of a carboxylicacid A₂ containing from 3 to 5 carbon atoms and exhibits an ethylenicunsaturation alpha to the carboxylic functional group, with an alcohol,preferably a saturated alcohol, of formula R₂ OH containing an averagefrom 11 to 15 carbon atoms, preferably from 12 to 14 carbon atoms, saidalcohol being advantageously lauryl alcohol,

of a percentage c (expressed on mass basis) of an ester of a carboxylicacid A₃ containing from 3 to 5 carbon atoms and exhibiting an ethylenicunsaturation alpha to the carboxylic functional group, with an alcohol,preferably a saturated alcohol, of formula R₃ OH containing an averagefrom 16 to 25 carbon atoms, preferably from 16 to 20 carbon atoms and,still more preferably, from 16 to 18 carbon atoms, said alcohol beingadvantageously cetyl alcohol, in which a is between about 12 and about20%, c is between about 14 and about 30% and b, which is between about72 and about 45% is such that a+b+c=100%.

For purposes of this invention, the term "lauryl alcohol" is defined asan alcohol mixture containing C₁₁ to C₁₆ alcohols, having a distributionof less than about a total of 3% by weight C₁₁ or lower and C₁₆ orgreater, about 20% C₁₂, about 30% each C₁₃ and C₁₄ and about 20% C₁₅,wherein the total is 100%. These have a mixture of linear and branchedalkyl groups.

For purposes of this invention, the term "cetyl alcohol" is defined asan alcohol containing C₁₄ to C₂₀ alcohols, having a distribution of lessthan about total of 6% of C₁₄ or lower and C₂₀ and greater, about 35-40%C₁₆ and about 60% of C₁₈ alcohols, with the total being 100%. Theseusually have an even number of carbon atoms and the alkyl groups areprimarily linear.

Sources of these alcohols include Alcool Gras 16/18 (Condea), Dobanol125L (Shell) and Alchem 125 (Erichem).

According to an advantageous embodiment the copolymers in accordancewith the invention

have a weight-average molecular mass (Mw) of between about 70,000 andabout 90,000 g/mole, preferably between about 80,000 and about 85,000g/mole, and

exhibit a polydispersity value Mw/Mn (ratio of the value of theweight-average molecular mass to the value of the number-averagemolecular mass) of between about 2 and about 5, preferably between about2 and about 3.

When the oil which is to be treated is at least partially naphthenic, ais between about 12 and about 20%, preferably between about 13 and about18% and still more preferably between about 14 and about 17%, c isbetween about 14 and about 25%, preferably between about 15 and about24% and still more preferably between about 16.5 and about 23.5% and b,which is between about 72 and about 45% is such that a+b+c=100%.

When the oil to be treated is a paraffinic oil c and b are between about14 and about 30% and between about 72 and about 53% respectively, abeing as defined above with a+b+c=100%.

The acids A₁, A₂ and A₃ may be different from one another but arepreferably identical; they may consist of mixtures, but are preferablysubstantially pure.

The acids A₁, A₂ and A₃ have advantageously 3 or 4 carbon atoms,methacrylic acid being preferred.

The radicals R₁, R₂ and R₃ may be pure or may consist of mixtures, itbeing understood that, preferably:

in the case of R₁ the quantity of propanol or of heavier alcohol doesnot exceed 10%, preferably 5% and, still more preferably 2%, by weight,

in the case of R₃ the quantity of alcohol(s) not containing 11 to 15carbon atoms does not exceed 10%, preferably 5% and, still morepreferably, 2% by weight,

in the case of R₃ the quantity of alcohol(s) not containing 15 to 25carbon atoms does not exceed 10%, preferably 5% and, still morepreferably, 2% by weight.

The radicals R₁, R₂ and R₃ are advantageously linear and, in any event,their branching content is lower than 50%, preferably lower than 25%.

The copolymers in accordance with the invention may be employed as theyare as viscosity improvers for the lubricating oils in question, thequantity of copolymers used corresponding to a proportion of about 2 toabout 20%, preferably from about 5 to about 15% and, still morepreferably, of about 7 to about 11% by weight of the mass of lubricatingoil to be treated.

It is convenient, however, to use them in the form of a compositioncomprising the copolymers of this invention with a normally liquidorganic diluent, preferably mineral oil, forming the reaction mediumwithin which the copolymerization is performed. The mineral oil may bethe same as the lubricating oil which is to be treated. The compositionin accordance with the invention normally comprises from about 25 toabout 75%, preferably from about 40 to about 75% by weight of at leastone copolymer in accordance with the invention, the remainder to 100%consisting essentially of a normally liquid organic diluent, preferablymineral oil.

The oils to be treated with the copolymers of this invention are oils oflubricating viscosity, including natural or synthetic lubricating oilsand mixtures thereof. Natural oils include animal oils, vegetable oils,mineral oils, solvent or acid treated mineral oils, and oils derivedfrom coal or shale. Synthetic lubricating oils include hydrocarbon oils,halo-substituted hydrocarbon oils, alkylene oxide polymers, esters ofcarboxylic acids and polyols, esters of polycarboxylic acids andalcohols, esters, of phosphorus-containing acids, polymerictetrahydrofurans, silicone-based oils and mixtures thereof.

Specific examples of oils of lubricating viscosity are described in U.S.Pat. No. 4,326,972 and European Patent Publication 107,282, both hereinincorporated by reference for their disclosures relating to lubricatingoils. A basic, brief description of lubricant base oils appears in anarticle by D. V. Brock, "Lubricant Base Oils", Lubricant Engineering,volume 43, pages 184-185, March, 1987. This article is hereinincorporated by reference for its disclosures relating to lubricatingoils. A description of oils of lubricating viscosity occurs in U.S. Pat.No. 4,582,618 (Davis) (column 2, line 37 through column 3, line 63,inclusive), herein incorporated by reference for its disclosure to oilsof lubricating viscosity.

The lubricating oil in accordance with the invention is one whichcomprises at least one copolymer in accordance with the invention in aproportion of from about 2 to about 20%, preferably from about 5 toabout 15% and, still more preferably, from about 7 to about 11% byweight of the mass of lubricating oil to be treated.

The conventional methods of radical copolymerization in solution inorganic diluent, preferably oil, can be used to prepare the copolymer inaccordance with the invention.

Such methods are described in the work "Encyclopedia of Polymer Scienceand Engineering" (H. F. Mark, N. M. Bikales, C. G. Overberger and G.Menges), 2nd edition (1988), published by Wiley Interscience.

These methods include free-radical initiated polymerization employingazo compounds or peroxides. Also described therein are photochemical andradiation initiated methods.

Useful initiators include organic peroxides, hydroperoxides and azocompounds.

Polymerization of acrylic and methacrylic monomers can take place undera variety of conditions, among which are bulk polymerization, solutionpolymerization, usually in an organic solvent, preferably mineral oil,emulsion polymerization, suspension polymerization and nonaqueousdispersion techniques.

Solution polymerization is preferred, especially in mineral oil diluent.This method is preferred for preparing polymers having molecular weightsin the range of from about 2000 to about 200,000.

Molecular weights of the polymers can be controlled employing a numberof techniques including choice of initiator, reaction temperature,concentration of monomers and initiator and solvent type. Chain transferagents can be used.

Molecular weights can be determined employing standard analyticalmethods such as gel permeation chromatography (GPC) using a polystyrenestandard.

Ionic polymerization techniques are known including cationic and anionicmethods; however, cationic methods are generally ineffective foracrylate and methacrylate monomer polymerization.

Free radical initiation is preferred.

Because acrylic polymerizations are usually accompanied by liberation ofconsiderable heat, care must be taken to avoid uncontrolled reaction.Temperatures can be controlled by using reactors with cooling jackets,controlling rates of addition and reaction solvents.

A typical procedure for preparing the polymers of this invention is tocharge at room-temperature about one third of the monomers, diluent,chain transfer agent and a portion of a peroxide initiator. The mixtureis heated to about 125° C. at which time heating is discontinued and thetemperature is allowed to rise exothermically, moderated with cold watercooling, to about 142° C. At this temperature, the remaining two-thirdsof monomer additional oil, chain transfer agent and a portion ofinitiator are added over about 1.5 hours. During this time cold watercooling is applied until the temperature drops to about 130° C. at whichexternal cooling is discontinued. The temperature then continues to dropuntil at the end of the 1.5 hour addition period, the temperature isabout 125° C. After monomer addition is completed the materials are heldat 125° C. for 0.5 hours, then four additional portions of initiator areadded at hourly intervals. After the final addition of initiator, thereaction mixture is held at 125° C. for 1 hour then diluted with oil tofinal concentration and filtered.

These methods were employed to prepare, on the one hand, 9 copolymers inaccordance with the invention and, for the purpose of comparison, 8copolymers in which the proportions a, b and c do not correspond tothose which the copolymers in accordance with the invention must have.

For the preparation of these 17 copolymers methacrylic acid was employedas acid and, as alcohol:

methyl alcohol for the copolymer based on R₁ OH.

lauryl alcohol for the copolymer based on R₂ OH.

cetyl alcohol for the copolymer based on R₃ OH.

The proportions

a% of ester E1 of methacrylic acid and of methyl alcohol

b% of ester E2 of methacrylic acid and of lauryl alcohol and

c% of ester E3 of methacrylic acid and of cetyl alcohol are shown below,in Table 1, for each of these copolymers (it being stated whether it isa copolymer in accordance with the invention or a copolymer studied byway of comparison).

Each of copolymer compositions 1-17 contains about 49.6% polymer in thediluent, which diluent is mineral oil, a paraffonic oil, 175N.

                  TABLE I                                                         ______________________________________                                                    PROPORTIONS IN %                                                  Copolymer   BY WEIGHT OF ESTER                                                No.         E1 (a%)     E2 (b%)  E3 (c%)                                      ______________________________________                                         1 (comparison)                                                                           8           88       4                                             2 (comparison)                                                                           32          64       4                                             3 (comparison)                                                                           8           64       28                                            4 (invention)                                                                            16          64       20                                            5 (invention)                                                                            16          64       20                                            6 (comparison)                                                                           12          60       28                                            7 (invention)                                                                            16          60       24                                            8 (invention)                                                                            12          64       24                                            9 (comparison)                                                                           12          74       14                                           10 (comparison)                                                                           15          75       10                                           11 (comparison)                                                                           8           88       4                                            12 (comparison)                                                                           32          64       4                                            13 (invention)                                                                            16          64       20                                           14 (invention)                                                                            16          64       20                                           15 (invention)                                                                            20          60       20                                           16 (invention)                                                                            12          60       28                                           17 (invention)                                                                            16          60       24                                           ______________________________________                                    

Note: Copolymer 6, having "c"=28, meets requirements for polymers ofthis invention. It is indicated as comparison because it was evaluatedin oil O₂, a naphthenic oil, in which polymers having a maximum `c` of25 are permitted.

The effect exerted on the viscosity of lubricating oils by theabove-mentioned copolymers was studied in comparison with threelubricating oils O₁, O₂ and O₃, respectively.

The first of these oils, namely oil O₁, consists of a mixture comprisingabout 60% by volume of a first essentially paraffinic oil (batch one)marketed by the Shell Company under the name "HVI60" and about 40% byvolume of an essentially naphthenic oil marketed by the Shell Companyunder the name "MV1N40".

The second of these oils, namely oil O₂, consists of a mixturecomprising about 60% by volume of a second essentially paraffinic oil(batch two) marketed by the Shell Company under the name "HVI60" andabout 40% by volume of the same essentially naphthenic oil (same batch)marketed by the Shell Company under the name "MVIN40".

The third of these oils, namely oil O₃, is a paraffinic oil marketed bythe British Petroleum Company under the name "150N".

In Table II below are shown some of the values at 40° C. and at 100° C.of the kinematic viscosities of the above-mentioned oils and of theirconstituents together with the values, for the same products, of thequantities VIE or "Viscosity Index Extension" defined in ASTM standardD2270 entitled Standard Practice for Calculating Viscosity Index fromKinematic Viscosity at 40° C. and 100° C. and consisting of an arbitrarynumber employed to characterize the variation of the kinematic viscosityof a petroleum product with temperature.

                  TABLE II                                                        ______________________________________                                        Viscosity (mm.sup.2 /s)                                                       HV160      HV160                                                              (batch 1)  (batch 2) MVIN40   O.sub.1                                                                             O.sub.2                                                                             O.sub.3                             ______________________________________                                         40° C.                                                                      27.0     24.7      8.6    17.10 16.26 31.0                              100° C.                                                                      5.01     4.75      2.35   3.70  3.58  5.2                               VIE   112      112       82     101   100   96                                ______________________________________                                    

Measurements were then carried out of the kinematic viscosity of theoils O₁, O₂ and O₃ at 100° C., 40° C., -15° C., -20° C. and -30° C., andthe VIE value was determined by introducing into these oils a proportionof 9% by weight of the various copolymers 1 to 17, prepared and definedas shown above.

A first set of measurements was performed with oil O₁ by employing thecopolymers 1 to 4.

The results are shown in Table III below.

                  TABLE III                                                       ______________________________________                                                 Kinematic viscosity of O.sub.1 (mm.sup.2 /s)                         Copolymer (No.)                                                                          100° C.                                                                          40° C.                                                                           -30° C.                                                                        VIE                                    ______________________________________                                        1 (comparative)                                                                          6.56      31.7      4210    168                                    2 (comparative)                                                                          6.19      26.7      4210    193                                    3 (comparative)                                                                          6.75      32.4      7970    173                                    4 (invention)                                                                            6.69      30.6      3850    185                                    ______________________________________                                    

The examination of the results assembled in Table III shows that, byvirtue of the copolymers in accordance with the invention, the viscosityat very low temperatures is markedly improved and is, in particular,found to be lower than 4000 mm² /s at -30° C. (this value of 4000 atvery low temperatures constituting an upper limit for the kinematicviscosity according to the oil manufacturers' specifications).

A second set of measurements was performed with oil O₂ employing thecopolymers 5 to 10.

The results are shown in Table IV below.

                  TABLE IV                                                        ______________________________________                                                 Kinematic viscosity of O.sub.2 (mm.sup.2 /s)                         Copolymer (No.)                                                                          100° C.                                                                          40° C.                                                                           -30° C.                                                                        VIE                                    ______________________________________                                         5 (invention)                                                                           6.58      29.0      3370    193                                     6 (comparative)                                                                         6.54      29.5      4000    186                                     7 (invention)                                                                           6.42      28.6      3330    188                                     8 (invention)                                                                           6.82      30.5      3540    193                                     9 (comparative)                                                                         6.58      29.5      4050    185                                    10 (comparative)                                                                         6.64      31.2      4150    177                                    ______________________________________                                    

The examination of the results assembled in Table IV shows that, byvirtue of the copolymers in accordance with the invention, the viscosityat very low temperatures is markedly improved and is, in particular,found to be lower than 4000 mm² /s at -30° C.

A third set of measurements was performed with oil O₃ employing thecopolymers 11 to 17.

The results are shown in Table V.

                  TABLE V                                                         ______________________________________                                                 Kinematic viscosity of O.sub.3 (mm.sup.2 /s)                         Copolymer (No.)                                                                          100° C.                                                                        40° C.                                                                          -15° C.                                                                       -20° C.                                                                       VIE                                 ______________________________________                                        11 (comparative)                                                                         9.43    55.6     2450   4860   153                                 12 (comparative)                                                                         8.94    47.9     5400   10070  170                                 13 (invention)                                                                           9.62    54.9     2060   3910   161                                 14 (invention)                                                                           9.57    54.4     2070   3910   162                                 15 (invention)                                                                           9.56    53.1     1990   3750   166                                 16 (invention)                                                                           9.57    55.3     2040   3850   158                                 17 (invention)                                                                           9.46    53.9     1990   3960   160                                 ______________________________________                                    

The examination of the results assembled in Table V shows that by virtueof copolymers in accordance with the invention, the viscosity at verylow temperatures is markedly improved and is, in particular, found to belower than 4000 mm² /s at -15° C. and at -20° C.

As a result thereof, copolymers of unsaturated fatty esters of the kindin question are available, whose constitution results sufficiently fromthe above to make it unnecessary to dwell further on this subject, andwhich exhibit many advantages in relation to those which already exist,especially that of imparting to the lubricating oils into which they areincorporated properties which are extremely valuable from the viewpointof kinematic viscosity at very low temperatures.

What is claimed is:
 1. A copolymer comprising carboxylic acid estercomprising a percentage a by mass of an ester of a carboxylic acid A₁containing from 3 to 5 carbon atoms and exhibiting an ethylenicunsaturation alpha to the carboxylic functional group, with an alcoholof formula R₁ OH containing from 1 to 3 carbon atoms;a percentage b bymass of an ester of a carboxylic acid A₂ containing from 3 to 5 carbonatoms and exhibiting an ethylenic unsaturation alpha to the carboxylicfunctional group, with an alcohol of formula R₂ OH containing on averagefrom 11 to 15 carbon atoms; and a percentage c by mass of an ester of acarboxylic acid A₃ containing from 3 to 5 carbon atoms and exhibiting anethylenic unsaturation alpha to the carboxylic functional group, with analcohol of formula R₃ OH containing on average from 16 to 25 carbonatoms in which a is between about 12 and about 20%, c is between about14 and about 30% and b is between about 72 and about 45%, such that a+b+c=100%.
 2. The copolymers as claimed in claim 1, havingaweight-average molecular mass Mw of between about 70,000 and about90,000 g/mole and which exhibit a polydispersity value Mw/Mn of between2 and
 5. 3. The copolymer of claim 1 wherein the alcohol R₁ OH contains1 or 2 carbon atoms.
 4. The copolymer of claim 3 wherein the alcohol R₁OH is methyl alcohol.
 5. The copolymer of claim 1 wherein the alcohol R₂OH contains from about 12 to about 14 carbon atoms.
 6. The copolymer ofclaim 1 wherein the alcohol R₃ OH contains from about 15 to about 20carbon atoms.
 7. The copolymer of claim 6 wherein the alcohol R₃ OHcontains from about 16 to about 18 carbon atoms.
 8. The copolymer ofclaim 2 having a weight average molecular mass Mw of between about80,000 and about 85,000 g/mole.
 9. The copolymer of claim 2 wherein thepolydispersity value Mw/Mn is from about 2 to about
 3. 10. A copolymerprepared by reacting in an organic diluent,a percentage a by mass of anester of a carboxylic acid A₁ containing from 3 to 5 carbon atoms andexhibiting an ethylenic unsaturation alpha to the carboxylic functionalgroup, with an alcohol of formula R₁ OH containing from 1 to 3 carbonatoms; a percentage b by mass of an ester of a carboxylic acid A₂containing from 3 to 5 carbon atoms and exhibiting an ethylenicunsaturation alpha to the carboxylic functional group, with an alcoholof formula R₂ OH containing on average from 11 to 15 carbon atoms:and apercentage c by mass of an ester of a carboxylic acid A₃ containing from3 to 5 carbon atoms and exhibiting an ethylenic unsaturation alpha tothe carboxylic functional group, with an alcohol of formula R₃ OHcontaining on average from 16 to 25 carbon atoms in which a is betweenabout 12 and about 20%, c is between about 14 and about 30% and b isbetween about 72 and about 45%, such that a +b+c=100%.
 11. The copolymerof claim 10 prepared employing a free-radical initiator.
 12. Thecopolymer of claim 10 prepared in a mineral oil solvent.
 13. Thecopolymer of claim 12 wherein the mineral oil is an oil of lubricatingviscosity.
 14. A composition comprising from about 25% to about 75% byweight of the copolymer of claim 1 and the balance comprising a normallyliquid organic diluent.
 15. The composition of claim 14 wherein thenormally liquid organic diluent comprises mineral oil.
 16. A compositioncomprising from about 25% to about 75% by weight of the copolymer ofclaim 10 and the balance comprises a normally liquid organic diluent.17. The composition of claim 16 wherein the normally liquid organicdiluent comprises mineral oil.
 18. A lubricating oil compositioncomprising a major amount of an oil of lubricating viscosity and fromabout 2 to about 20% by weight of the copolymer of claim
 1. 19. Alubricating oil composition comprising a major amount of an oil oflubricating viscosity and from about 2 to about 20% by weight of thecopolymer of claim
 10. 20. A partially naphthenic lubricating oilcomposition comprising at least one copolymer as claimed in claim 1 in aproportion of from about 2 to about 20% by weight of the mass oflubricating oil to be treated, said copolymer being such that a isbetween about 12 and about 20%, c is between about 14 and about 25%, andb is between about 72 and about 45%, such that a+b+c=100%.
 21. Apartially naphthenic lubricating oil composition comprising at least onecopolymer as claimed in claim 10 in a proportion of from about 2 toabout 20% by weight of the mass of lubricating oil to be treated, saidcopolymer being such that a is between about 12 and about 20% c isbetween about 14 and about 25%, and b is between about 72 and about 45%,such that a+b+c=100%.
 22. A paraffinic lubricating oil which comprisesat least one copolymer as claimed in claim 1 in a proportion of fromabout 2 to about 20% by weight of the mass of lubricating oil to betreated, said copolymer being such that c and b are between about 14 andabout 30% and between about 72 and about 53% respectively, a beingbetween about 12 and about 25% with a+b+c=100%.
 23. A paraffiniclubricating oil which comprises at least one copolymer as claimed inclaim 10 in a proportion of from about 2 to about 20% by weight of themass of lubricating oil to be treated, said copolymer being such that cand b are between about 14 and about 30% and between about 72 and about53% respectively, a being between about 12 and about 20% witha+b+c=100%.